Investigation of the nitrogen fixation process in atmospheric pressure nanosecond pulsed discharge via time-resolved LIF/TALIF diagnostics

Abstract Atmospheric pressure non-equilibrium plasmas enable nitrogen fixation (NF) by efficiently breaking the N ≡ N bond of N 2 , offering a sustainable alternative to the energy-intensive Haber–Bosch process. Nanosecond pulsed (nsP) discharges provide enhanced control over breakdown dynamics and plasma chemistry, yet the mechanistic roles of pulse width and gas composition in NF remain unclear. In this work, we investigate atmospheric pressure needle-to-needle nsP discharges using laser-induced fluorescence (LIF) and two-photon absorption LIF to measure time-resolved absolute densities of atomic nitrogen (N), atomic oxygen (O), and nitric oxide (NO) under varying pulse widths (100–300 ns) and N 2 /O 2 ratios. Complementary Fourier transform infrared spectroscopy measurements are performed to quantify NO, NO 2 , and total NO x concentrations, providing a basis to calculate NF energy costs from the measured average discharge power. Results show that energy injected during different discharge stages contributes unequally to NF: the breakdown stage exhibits the highest energy cost, while the plasma maintenance stage delivers the highest NO yield per unit energy. Increasing pulse width enhances NO production and reduces energy cost by extending the maintenance stage. Gas composition strongly influences performance: the optimal mixture (N 2 /O 2 = 50/50) yields the highest NO concentration and lowest energy cost due to a favorable balance of N and O atom densities. In contrast, N-rich mixtures (95/5) show suppressed NO formation, while O-rich mixtures (10/90) fail to achieve high NO yields due to insufficient nitrogen intermediates. These findings reveal that suppressing N-driven NO decomposition and enhancing O-assisted NO formation are key to improving NF efficiency. The mechanistic insights and diagnostic methodology provide a basis for optimizing nsP-NF operating conditions for sustainable plasma-based NF.